Conventional fire fighting in enclosed spaces employs a foam or powder where fire fighting with water is not feasible or prohibited. Thus, heretofore Halon.RTM. has been used as a fire extinguishing agent. However, the use of Halon.RTM. has been prohibited officially and has been replaced by the use of an inert gas for reducing the oxygen content. The inert gas is blown into the enclosed space where the fire is occurring in order to reduce the oxygen content of the atmosphere in the enclosed space to a level that will not sustain the fire. For this purpose, the oxygen content of the air in the enclosed space should be reduced to below 15%, preferably below 12% by volume.
It has been considered to use as a source for an inert gas a propellant which generates during its reaction waste gases having a high nitrogen content. However, such waste gases generally also contain other components in addition to nitrogen, namely carbon dioxide CO.sub.2 that may amount up to 20% by volume. Such a carbon dioxide content provides a problem if people are in the enclosed space in which the fire started. The problem becomes even more pronounced when the people in the enclosed space should not leave the compartment, such as a subway compartment or when they cannot leave the compartment, such as an aircraft cabin in flight. Due to the noxious effect of increased concentrations of carbon dioxide in the breathing air, it is necessary to avoid further increasing the carbon dioxide concentration in the breathing air, which due to the fire already has an increased content of carbon dioxide even without adding carbon dioxide generated by a fire extinguishing gas. Another disadvantage of propellants as a source for fire extinguishing gases is seen in that the reaction gases generated by such propellants frequently also contain carbon monoxide (CO), (H.sub.2), and methane (CH.sub.4) which are in fact combustible components that should not be supplied to the fire. A further disadvantage of the use of propellants as a source for a fire fighting inert gas is seen in that the combustion of these propellants also results in the formation of dust in the form of slag or cinders. Such dust can amount up to 40 weight percent of the propellant mass.
It has also been suggested to use as a source for the production of an inert fire fighting gas, solid propellants on the basis of sodium azide (NaN.sub.3). Such solid propellants are used, for example in miniaturized form for inflating air bags in a vehicle. These solid propellants have the advantage that the reaction product is approximately pure nitrogen. However, the use of such solid propellants for fire fighting purposes is not feasible, especially on a larger scale due to the toxicity of the starting product for making the solid propellants. Furthermore, the combustion of these solid propellants produces corrosively acting and health impairing dusts which must be either collected before they can cause damage or which must be neutralized.
The use of solid propellants has yet another disadvantage, namely that once ignition has started, a complete combustion takes normally place so that a repeated ignition, for example when the fire should restart although it has been assumed that it was extinguished, is then not possible other than using a new propellant set. Furthermore, the use of inert gas generating systems with solid propellant generators would require the use of a multitude of modular generators in those instances where larger enclosed spaces or even entire building tracts are to be included in a fire extinguishing pipe network. Thus, a multitude of individual generators and respective connections would have to be installed in a system of such an inert gas distribution pipe network.